This invention relates to an aperture auxiliary brake control device in a camera which can selectively employ a shutter priority automatic exposure (EE), an aperture priority automatic exposure (ES) and a manual exposure mode of operation.
In a conventional aperture control type automatic exposure camera, light from an object, passes through the opening of the aperture, is measured while the aperture of the lens is being stopped down from the full-aperture, and when the aperture opening is stopped down to an aperture value suitable for predetermined shutter spaced and film sensitivity, the aperture stopping-down operation is stopped. This automatically determines the aperture opening. If in this conventional camera the stopping-down operation is carried out only with the lens, then the operation time required for stopping down the full-aperture to the suitable aperture value is too short to terminate the stopping-down operation with high accuracy. In order to overcome this difficulty, a speed slowing mechanism is interlocked with an operating member which is operated in association with the stopping-down operation.
However, the amount of movement of the aperture release plate of the lens is, in general, relatively small for aperture values close to the minimum aperture value. Therefore even if a speed slowing mechanism for moving the aperture release plate substantially at an equal speed is interlocked therewith, the quantity of light is abruptly changed for aperture values close to the minimum aperture value. Accordingly, in the case when the aperture release plate of the lens is moved substantially at an equal speed and the time required for stopping down the aperture from the full-aperture is not sufficiently long, the time per EV becomes excessively short for aperture values close to the minimum aperture value. Therefore, it is difficult to achieve the control with high accuracy.
However, if the above-described operating time is sufficiently long, the time interval which elapses from the release of the camera until the operation of the shutter starts also becomes long. Accordingly, in this case, the photographer may not be able to take for example a high speed picture he desires because the shutter will run after the picture has taken place. In order to overcome this drawback, a brake member is provided to apply a brake force to the speed slowing mechanism before the operation of the speed slowing mechanism is terminated.
On the other hand, if the correct aperture value is obtained while the lens is stopped down from the full-aperture to the minimum aperture value, the stopping-down operation is stopped when the correct aperture value is obtained. Simultaneously, the top curtain is unlocked to run, and the exposure is carried out. However, in the case where the correct aperture value cannot be obtained even if the stopping-down operation is carried out from the full-aperture to the minimum aperture value, no signal for stopping the stopping-down operation is provided. Therefore the top curtain is not unlocked to run and the operation of the camera is stopped.
In order to eliminate this difficulty, an interlocking timer circuit is provided which releases the locking of the top curtain a short time after the lens stopping-down operation is completed. This interlocked timer circuit will operate in the aperture priority automatic exposure or in the manual exposure since, in these two modes the aperture is not controlled. The time set by the interlocking timer is somewhat longer than the stopping-down operation time in order to reduce the delay in shutter operation. However, it is impossible to make the set time any longer. In a situation where the lens stopping-down operation becomes slow because the lens is used at a low temperature such as -20.degree. C. or -30.degree. C. or it is old, sometimes the lens stopping-down operation is stopped by the interlocking timer before the lens is stopped down to the minimum aperture value. In the (EE) operation where the aperture is controlled, an aperture value of F11 may be, in practice, instead of the correct value of F22. However, in the (ES) operation or manual exposure modes in which an aperture value has been specified, the aperture value has been intentionally set to by the operation F22. Therefore, if the aperture value is not the proper value, F22, but F11 in the (EE) mode, then the depth of field is changed greatly, and the intended picture cannot be obtained.